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Coefficient Quantization

The coefficients in a band are all quantized with the same step size Q. The Q is predicted from the last mask, and the residual Qr is encoded as


and thereafter Huffman encoded. The Q controls a nonuniform coefficient quantizer, with the following characteristic.


where a c=1.3 has proved to work well. A nonuniform quantizer does not follow the masking threshold theories in section 3.4, but works very well -- it is used in e.g MPEG-2 AAC [2].

The coefficients of any orthogonal linear transform can be quantized as described above, since


and so the quantizer makes no difference between the coefficients from the different modes in section 4.2.2.

Bosse Lincoln
Sat Mar 7 16:27:43 PST 1998